Linear induction control system

ABSTRACT

A control system is employed in a linear induction propulsion system of the type having linear induction primary elements which are fixedly mounted at spaced intervals along a guideway and linear induction secondary structures which are carried by respective movable structures driven along the guideway by the propulsion system. Sensing devices are provided for detecting proximity of the linear induction secondary structures to respective ones of the primary elements, and apparatus is provided for conducting electrical power to any of the primary elements which are in alignment with any portion of one of the secondary structures. The control system is operable to regulate the spacing between successive movable structures.

Umted States Patent 1191 1111 3,792,665

Nelson Feb. 19, 1974 [54] LINEAR INDUCTION CONTROL SYSTEM FOREIGNPATENTS 0R APPLICATIONS Inventor: Roy Nelson, Grand Prairie, 842,0906/1939 France 310 13 [73] Assignee: LTV Aerospace Corporation, Dallas,662,682 8/1929 France 104/148 LM Tex. Primary ExaminerDuane A. RegerFlledl 1972 Assistant Examiner-Galen L. Barefoot [21] Appl NO 281,262Attorney, Agent, or FirmJames M. Cate; H. C.

Goldwire [52] US. Cl. 104/148 LM, 318/135 51 Int. Cl B61b 13/12 [57]ABSTRACT 5 i l f Search 104 143 MS, 14 LM, 4 5; A control system isemployed in a linear induction 313/135; 310/12 13; 24 /110 10 1propulsion system of the type having linear induction A primary elementswhich are fixedly mounted at spaced 5 References Cited intervals along aguideway and linear induction secon- UNITED STATES PATENTS darystructures which are carried by respective movable structures drivenalong the guideway by the proat 33 2 pulsion system. Sensing devices areprovided for de- 3407749 10/1968 Ffig 318/135 tecting proximity of thelinear induction secondary 3 403 634 10/1968 cm;v';i;;III........ will.310/12 Structures to espective ones of the Primary elements 31541;,75112 1970 lzhelya etal 104/148 LM and apparatus is Provided for conductingelectrical 2,794,929 6/1957 Adamski 104/148 LM p wer to any of theprimary elements which are in 3,555,380 1/1971 Hings...;....., 318/135alignment with any portion of one of the secondary 3,712,240 1/1973Donlon et a1. 104/1 LM structures. The control system is operable toregulate 3,547,041 12/1970 fl 6! 1104/148 LM the spacing betweensuccessive movable structures. 573,823 12/1896 Leffler 310/12 2,618,74111/1952 Jacobs et al. 246/161 4 Cl im 9 Drawing Figures 1 I W 1 1 1H1011 :5 Tffflifhi I 111111 I I I I I Q) l I8 1 I a a 1' mm "1"" I.

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c .Emimmm mm E LINEAR INDUCTION CONTROL SYSTEM This invention relates tolinear induction propulsion systems and, more particularly, to a controlsystem for a linear propulsion system having stationary primary elementsand movable secondary elements.

Linear induction propulsion systems have been proposed fortransportation systems of various types, such as high speed trainsystems and mass transit systems. A majority of the linear inductionpropulsion systems proposed for use in public transportation systemshave been of the fixed secondary, movable primary type in which vehiclespowered by the propulsion systems carry LIM (linear induction motor)primary elements, the primary elements being energized by electricalpower conducted to the vehicles from a remote power source. Such anarrangement has been preferred because it has been thought to be moreeconomically feasible than the movable secondary, fixed primary systemswherein the LIM secondaries are carried by the vehicles, primarilybecause of the elimination, in the former, of the requirement for amultiplicity of primary elements installed at successive intervals alongthe guideway, track, or roadway along which the LIM powered vehiclestravel. Such fixedly mounted, LIM primary elements include coils ofrelatively high power handling capacity, often of heavy copper wire, andthey thus represent a major investment if they must be extended along alarge percentage of the length of a guideway. As is known in the art,the secondary elements of fixed secondary LIM systems may be constructedas elongated, vertical rails or strips, often including laminations offerromagnetic and electrically conductive materials extended along thelength of the guideway. Such elongated secondary structures may beconstructed less expensively than LIM primary elements which areextended continuously along the length of a guideway.

While the linear induction propulsion systems employing fixedsecondaries thus provide some advantages for certain applications, theyalso suffer from a number of disadvantages when compared with the fixedprimary systems. One obvious disadvantage is that, in the fixedsecondary systems, motive power for energizing the primaries isconducted to the moving vehicles by means such as electrical brushelements slidably associated with power rails extended along theguideway or track, according to practices well known in the art.Inherent in such sliding contact power supply systems are a number ofundesirable features. These include the necessity for protectingbystanders from accidental contact with the power rails or wires whileat the same time permitting accessibility thereto by the brushes orother contacting means. Another problem relates to malfunctions whichmay occur during extremes of weather conditions, e.g., when rain, snow,ice, or blown dust affects contact with the power rails or wires. Anundesirably great amount of preventive maintenance of the brushelements, and of the flexible linkage structures which support thebrushes in contact with the power rails, is required if failures are tobe minimized. Additionally, control signals must be transmitted to thevehicles for regulating the traffic flow and spacing of the vehiclesalong the guideway is centralized or remote control of traffic flow isdesired, as it normally is in high capacity systems.

In contrast, the fixed primary LlM systems avoid many of thedifficulties and expenses related to power distribution and trafliccontrol by eliminating the need for the conduction of electrical powerand control signals to the vehicles. That is, the LIM primary elementsand the required, electrical power distribution systems are fixedlymounted, e.g., within or alongside the guideway or roadway, and may becompletely enclosed to prevent accessibility to the public or exposureto extremes of weather. The only necessary relationship between the LIMprimary elements and the vehicles is that of the magnetic flux betweenthe primaries and the secondary structures on the vehicles when theprimaries and secondaries are in mutually confronting relationship.

Headway control and velocity regulation in continuously circulative, LIMpowered systems has, in the past, involved control systems wherein thespacing and velocity of the vehicles is regulated by means of extensive(and expensive) electrical control apparatus. Two general approaches tothe problem may be taken. If only very low speed operation is required,relatively unsophisticated and inexpensive control apparatus may besafely employed. If the pole pitch of the UM primaries is uniform, alongthe length of the guideway, and the applied AC current is of a constantfrequency, the vehicles naturally tend to travel at a uniform velocityand to thus maintain a given initial spacing. Some variation in drag isalways encountered, however, which causes a variation in slippage, ordeviation in the velocity of respective vehicles from the constant,syncronous speed to which the vehicles are urged by the LIM primaries,and the vehicles may therefore eventually overtake one another.Collisions at speeds below approximately 5 mph may not be unacceptableif appropriate, spring biased bumpers or the like are provided for thecars. At higher velocities, however, more sophisticated controls arerequired. Such controls must not only be fail safe with respect to theprevention of collisions between successive vehicles, but also must beoperable to accelerate and decelerate the the vehicles at rates ofacceleration which do not exceed those acceptable from the standpoint ofdesired minimum standards of passenger comfort.

With respect to the improvement of standards of safety and reliabilityfor such systems, it is desirable that the control and braking of thevehicles be performed by mechanisms which are not subject todeterioration because of exposure to various weather conditions and toexcessive vibration and stress. Therefore, it is believed preferablethat control and braking of the vehicle be accomplished by fixed primaryelements and associated circuitry mounted along the guideway rather thanby sliding power contact means and control apparatus carried by thevehicles. As will be explained in the description to follow, trafficregulation and headway control can be accomplished, in the fixed primarysystem disclosed herein, by means of control elements contained entirelywithin sealed facilities fixedly mounted along the guideway.

As has been suggested, the expenses associated with installingextensive, fixed primary, LIM propulsion systems have been a majorfactor in preventing general use of such systems in the past, in spiteof the several advantages, outlined above, which are inherent in suchsystems. As also suggested above, a major expense in the fixed primarysystems has been that of the LIM primary elements extended alongsubstantial portions of the guideway. In the past, attempts have beenmade to minimize this expense by spacing the primaries along theguideway rather than extending them continuously along the guideway.This technique has presented further problems, however, in that, in suchsystems, the vehicles so propelled tend to accelerate and decelerate inan objectionable manner as they pass from one primary to the nextbecause of variances in the total magnetic flux action upon the LIMsecondaries carried by the vehicles.

A further economic disadvantage associated with prior, fixed primary LIMsystems relates to the excessive power consumption of such systems.Prior art systems often entail the conduction of operating power to anumber of the primary elements, although only those which areinteracting with the secondaries of adjacent vehicles are performinguseful work at a given instance. In contrast, of course, there is nosuch inefficiency in the fixed secondary systems, since the LIM primaryon a vehicle of such a system is continuously operable to magneticallyinteract with a corresponding, adjacent region of the secondarystructure.

It would obviously be a great advance in the art if the advantageousfeatures, outlined above, of fixed primary, linear induction systemscould be achieved in a system in which the inefficiencies ofpresent,fixed primary LIM systems, such as excessive power consumptionand high initial costs, were minimized.

It is, accordingly, a major object of the present invention to provide anew and improved, linear induction propulsion system having fixedprimary induction elements.

Another object is to provide such a propulsion system in which powerdistribution and traffic control is accomplished by fixedly mountedcomponents, independently of control devices aboard the vehicles.

Yet another object is to provide such a system in which powerconsumption is reduced greatly from that required in previous, fixedprimary systems.

A still further object is to provide such a propulsion system in whichthe initial cost of the system is minimized by mutual spacing of theprimaries along the guideway or track of the system, yet wherein thevehicles receive a substantially constant propulsive force as theyprogress forwardly, whereby objectional acceleration and deceleration ofthe vehicles is prevented.

Another major object is to provide a reliable system having theabove-cited advantages which is additionally of practicable andeconomically feasible construction.

In the drawing:

FIG. 1 is a side elevation, partially diagrammatic in form and partiallycutaway, ofa vehicle carrying a LIM secondary structure constructedaccording to a pre ferred embodiment of the invention, and showing aportion ofa guideway containing two LIM primary elements installedaccording to the preferred embodiment;

FIG. 2 is a plan view of the secondary structure of FIG. 1 showing thepivotable linkages thereof;

FIG. 3 is a view of the apparatus of FIG. 2 with portions of theframework cut away;

FIG. 4 is a diagrammatic representation of the clutch mechanism employedby the vehicles in the preferred embodiment of the system;

FIG. 5 is a plan view, in diagrammatic form, showing the relativespacing of the LIM primary elements of the preferred embodiment of FIGS.1-3;

FIG. 6 is a plan view, similar to FIG. 5, showing an alternativeembodiment;

FIGS. 7-9 comprise a schematic and block diagram of a preferredembodiment of the traffic control systems of the linear inductionpropulsion system.

With initial reference to FIG. 1, a linear induction propulsion system10 constructed according to a preferred embodiment of the invention isemployed for propelling a wheeled vehicle 11 along a guideway 12. Thepropulsion system 10 is suited for use in any transportation system inwhich movable structures are con strained to travel along a fixedpathway or guideway. To illustrate other, alternative embodiments (notshown), the movable structures 11 may, for example, comprise railwaycars, cargo or baggage containers adapted to follow a slideway or chute,or wheeled vehicles; alternatively, vehicles supported by magneticlevitation or by ground-effect air cushion devices or the like may beemployed. The guideway followign vehicles 11 of the illustrated systemare therefore presented herein or illustrative purposes only.

The exemplary, guideway following vehicle 11 is of the type havingsteerable wheels 13 suitably provided with resilient rubber tires 14.The vehicle 11 is adapted to automatically follow the guideway 12 bymeans of internal steering mechanisms (not shown) connected toguidewheel assemblies 15 as shown in FIG. 2. Each guidewheel assembly 15suitably comprises two, horizontally alighed guidewheels 16 which aremounted to straddle a vertical, upright guide rail 17 extended alongsideand parallel to the supporting surface of the guideway 12. The steeringmechanism, responsive to horizontal input signals received from theguide wheel assemblies 15, acts to steer the vehicle 11 along theguideway 12 during movement of the vehicle in a first, or forwarddirection along the guideway as indicated by the arrow 18. Other,analogous guideway systems, for example, have employed U-shaped concreteguideways (not shown) in which vehicles are guided by opposing,centrally facing guide walls extending alongside the roadway. Theconstruction of such guideway systems and guideway following vehicles isgenerally known, and further description thereof is therefore notconsidered necessary here. The vehicle 11 will be recognized by those inthe art as being of the PRT (personal rapid transit) class fortransporting individual or small groups along selected or selectableroutes in a controlled manner.

As shown in FIG. 2, a LIM secondary structure 20 is connected to thevehicle 11 for propelling the vehicle along the guideway 12, as will beexplained in detail in the description to follow. The LIM secondarystructure 20 preferably includes several LIM secondary elements 21arranged end-to-end in tandem, in a manner also to be describedhereinbelow. The secondary elements 21 are suitably for the typesupplied by the SACM&G division of the General Electric Company,Nashville, Tenn., under Part No. 153 B 3900 AA. These LIM secondaries 21are in the general form of a slab of approximately rectangular plan andhaving a horizontal lower surface which is substantially flat. Thesecondary elements 21 are mounted in longitudinal alignment with theguideway 12 and each has first and second end portions 23, 24 (FIG. 2)directioned in the first direction,

indicated by arrow 18, and in a second, opposite direction,respectively. The above identified secondaries 21 are formed ofmultiple, vertical sheets of ferromagnetic material disposed side byside and extending from the first to the second end portions 23, 24 ofthe secondary elements 21, laticed with transversely extending,horizontally disposed aluminum members inserted through theferromagnetic sheets. As is known in the art, other constructions andtypes of secondary elements are available which function in an analogousmanner. According to the preferred embodiment of the invention, asupporting framework 25 is provided for carrying the UM secondaryelements 21. With additional reference to FIG. 3, the framework 25consists of three frame structures 26 bolted to transverse supportmembers 27 which are attached to and extend over the upper side of theLIM secondary elements 21. The frame structures 26 are equipped withwheels 28, suitably of a relatively hard, plastic or rubber material,for supporting the framework 25 and the secondary elements 21 above andin horizontal alignment with the surface of the roadway of the guideway12. Wheels 28 are provided at the first and second, i.e., the front andrear end portions 23, 24 of each secondary element 21, and eight wheels28 are thus provided for the illustrated embodiment employing threesecondary elements 21. To prevent excessive friction between the wheels28 in turns, the frontmost and rearmost wheels 28A, 13 are connected tothe respective frame structures 26 by means of respective, rotatablecaster supports 29A, 298. The three frame structures 26 are alignedlongitudinally by means of first and second hinge connections 30, 31positioned adjacent the confronting end portions 23, 24 of thesecondaries 21. At each hinge connection 30, 31, vertical,interdigitating tab elements 32 are extended forwardly from the forwardends of the respective frame structures 26 and rearwardly from the rearend portions, and positioned side by side in horizontal alignment.Horizontal, left and right axles 33, 34 are extended transversely of thevehicle 11 through corresponding bores formed through the tab elements32, and the four, central, framework wheels 28 are co axially androtatably mounted on outwardly projecting end portions of the axles 33,34. The hinged connections 30, 31 permit the secondary structure to bendvertically, at the hinged connections, when the vehicle 11 is travelingover irregular portions of the guideway 12 and when it travels fromlevel sections onto upwardly or downwardly sloped portions of theguideway. This articulated construction of the secondary structure 20permits the secondary elements 21 to be positioned in close proximitywith primary elements (to be described) installed in the guideway 12,yet allows the vehicle 11 to travel safely over guideways having somedegree of irregularity. Thus, the expense related to construction of theguideway 12 is reduced, in that precise and level construction thereofis not required. The hinged construction of the secondary structure 20also permits the effective length of the secondary on each vehicle 11 tobe extended to the full length of the vehicle, as shown, or even tosomewhat more than the length of the vehicle, which provides furtheradvantages which will become apparent from the description to follow.

Connection between the secondary structure 20 and the vehicle 11 ispreferably made by means 35 permitting relative vertical movementbetween the vehicle 11 and the secondary structure 20 but preventingsubstantial relative horizontal movement therebetween. In the preferredembodiment, upstanding, vertical posts 36, 36A are welded or otherwiserigidly affixed to front and rear portions of the framework 25.Corresponding openings are formed through respectively adjacent portions37 of the vehicle 11 in register with the adjacent posts 36, 36A forslidably receiving the respective posts. Preferably, one of the posts36A is received in a circular bore formed vertically through the vehicleframe portion 37, while the other post 36 is slidably received in a slot38 formed through the frame portion 37 and extending parallel to thelongitudinal axis of the vehicle 12. Forward and rearward forcesreceived by the LIM secondary elements 21 are thus transmitted to thevehicle 1 1 through the rear post 36A, while the forward post 36 isslidable forwardly and rearwardly within groove 38 and therefore doesnot transmit such forces to the vehicle, although it does serve toprevent relative movement of the secondary structure 25 transversely ofthe vehicle 11 and thus keeps the secondary structure in properalignment with the guideway 12 and with the primary elements 40 to bedescribed. The reason for this arrangement is that, as the flexibleframework 25 travels over irregular surfaces and flexes at its hingedconnections 30, 31, some variance of its overall length occurs, andcompensation therefor is thus provided by the slot 38. Respective capsor bosses 38 are formed on the uppermost portions of the posts 36, 36Afor retaining the posts 36 in the frame portion 37. The connecting means35 thus permits relative vertical movement of the vehicle 11 and thesecondary structure 20, yet can transmit forward or rearward drivingforces on the vehicle. Accordingly, the vehicle 11 can be provided witha suitable suspension system for providing a relatively soft ride forthe vehicle even though the secondary structure 20 is provided with arelatively rigid suspension for resisting the substantial, downwardlydirected magnetic forces which are exerted upon the secondary elements21 during operation;

Referring again primarily to FIGS. 1 and 2, a plurality of linearinduction primary elements 40 is also provided, each primary element 40being fixedly mounted within a corresponding chamber 41 depressed belowthe upper surface of the guideway 12, each LIM primary element beingpositioned with its upper surface depressed slightly below the surfaceof the guideway 12. The primary elements 40 are suitably covered byhorizontally disposed sheets 42 of magnetically permeable materialmounted contigously with the surface of the guideway 12 for protectingthe primary structures, and the circuitry connected to the primarystructures, from environmental conditions and vandalism. The LIMprimaries 40 are suitably of the type manufactured by the GeneralElectric Company at its Nashville facility under part number 149 C 4200AG, these primaries having approximately l5O pounds of stall thrustcapacity.

Referring now to FIG. 5, the LIM primary elements 40 are mutually spacedalong the guideway 12 and have respective first and second, i.e., frontand rear end portions 44, 44A, 44B; 45, 45A, 45B directed in the firstand second or forward and rearward directions, respectively, along theguideway 12. The direction indicated by arrow 18 again is to beconsidered the normal direction of travel for the vehicle 12. Eachrespective first end portion 44B of each primary element 40B ispreferably spaced, by a uniform distance in the first direction alongthe guideway 12, from the first end portion 44A of a respective,corresponding primary element 40A, each pair 49 of corresponding,mutually spaced primary elements 408, 40A; 40A, 40 in at least a portionof the guideway 12 being of substantially the same length, for reasonswhich will become apparent. Each secondary structure 20, in thepreferred embodiment, has a total length substantially equal to theuniform distance between the first end portions 448, 44A of acorresponding primary elements 408, 40A. In the embodiment of FIG. 5,the corresponding primary elements 40, 40A are successive, and thuscomprise a pair 49 of successive elements. Primary element 40A and thenext successive primary element 40B comprise a second pair ofcorresponding primaries, it being thus shown that the secondarystructure 20 will pass over the rear portion 458 of the forward primaryof any correspond ing pair as it passes the rear portion 45A of therearmost primary of the pair. In an alternate embodiment as shown inFIG. 6, for example, the primary elements 40 of respective pairs 49 ofcorresponding primary elements are not successive; rather, the frontmostprimary element 46 of a first pair 48 is positioned forwardly of therearmost primary element 40 of a second pair 49. In this example, theprimary elements 46 of the first pair 48 are larger and more powerfulprimary elements than those of the second pair 49 and are suitable forassisting the second pair 49, for example, in powering the vehicle 11 upinclined portions of the guideway 12. In the embodiment shown in FIG. 5,the length of each secondary structure 20 is greater than twice thelength of the primary elements 40, 40A; 40A, 40B or pairs ofcorresponding primaries. Thus, as advantageously per mitted by thedisclosed system, the primary elements 40 need to be extended along onlya small percentage of the total length of the guideway 12 in normalinstallations. The primaries (40, 40A; 40A, 40B) of respective pairs 49of corresponding primaries are corresponding in the sense that they bothreact with a single one of the secondary structures 20 when the frontand rear portions of the secondary are positioned in register with theprimaries of a respective pair, as will be described with respect to theoperation of the system.

With respect now to the circuit diagram of FIGS. 7, 8, and 9, threesuccessive segments [n, (n l), and (n 2)] of the control circuit 51 ofthe propulsion system are shown in FIGS. 7, 8, and 9, respectively.First, second, and third proximity sensors 52, 52A and 52B arepositioned immediately forward of first, second and third LIM primaries40, 40A, and 408 (corresponding to the identically numbered elements ofFIG. 5) respectively, in guideway segments n, (n l), and (n 2). Theproximity sensors 52, 52A, and 52B are spaced forwardly in the guidewayfrom the respective LIM pri maries 40, 40A, and 40B by about 4 to 6inches and comprise sensing means, adjacent each primary element 40,40A, 40B, for sensing the proximity to the respective, correspondingprimary elements 40, 40A, and 40B, of one of the secondary structures(FIG. 1) on one of the vehicles 11. The sensors 52, 52A, 52B aresuitably for the ferromagnetic, reed switch type, such as thatmanufactured under part number 4FRl-6 of the Micro Switch Company, andare operable to close a normally open switch 53 when a mass offerromagnetic metal, e.g., that of one of the secondary structures 20,passes over the sensor. Alternatively, they may be of the mechanicaltrip switch type, the inductive coil type, or any other suitable type.

To briefly summarize the control circuit 51, each proximity sensor 52,52A and 52B is connected in series with the coil of a corresponding,proximity relay (54, 54A, and 54B, respectively) whose function is toactuate a corresponding, power control relay 56, 56A, and 5613,respectively, to supply power successively to LIlVl primaries 40, 40A,and 408, respectively if forward progress of the vehicle lll (FIG. 1) isappropriate. Each segment n (n l), (n 2) of the circuit 51 is connectedbetween a respective one of the power control relays 56, 56A, 56B and arespective LIM primary 40, 40A, 40B for reversing the polarity of powersupplied when emergency braking of a vehicle is required.

More specifically, and with respect now to the circuit of the first or nth segment illustrated in FIG. 7 the proximity sensor 52 includes anormally open switch 53 connected in series between a grounded point 58and, via lead 59, to one side of relay coil 60 of the first proximityrelay 54. The proximity relay 54, and the corresponding proximity relays54A, 54B of the other two segments, are suitably of the single throwtype, having first and second, normally open switch elements 61 and 62.Relays of the general type typified by Model 8501- C2 manufactured bySquare D Company are exemplary of the type employed as proximity sensorrelays 54, 54A, 5413, although only two poles are necessary for theillustrated embodiment.

While relay controlled switching elements, e.g., relays 54, 54A, 54B and56, 56A, 56B, are shown in the drawings, it will be understood by thoseskilled in the art that solid state switching devices of various typesmay be substituted therefor if desired, according to practices known inthe art.

A power source 64 for suppling 440 -volt,3 -phase power to the system isprovided, and 3 -phase voltage therefrom is conducted to segments n, (n1), (n 2) through a power cable 65, comprising power bus wires 65A, 65B,and 65C. A voltage reducing transformer 67 has a primary windingconnected to the power source 64 and a secondary winding connected, onone side, to a ground 68 and on the other side to a lead 69 whichconnects to a rectifying, DC power supply circuit 72 for rectifying ACpower from the reducing transformer 67. The DC output of DC power supply72 is conducted through a power supply conductor" 73 to the severalsegments of the circuit 51.

Upon actuation of the proximity sensor 52 by an adjacent secondarystructure 20 (FIG. 1) passing over the sensor 52, the normally openswitch 53 of the sensor 52 is closed, thus completing a circuit from DCsupply conductor 73 and lead 74, through the coil 60 of proximity relay54, through lead 59 and switch 53 to the grounded point 58. Thiscompleted circuit loop results in the current flow which actuates theproximity relay 54 to close normally open switch elements 61, 62thereof. Positive potential is then conducted from DC power supply 72through DC supply wire 73, successively through leads 74 and 75, throughswitch element 61 and through lead 76 to the coil 77 of power relay 56.The other side of coil 77 is normally connected to ground, successivelythrough leads 79 and 80, lead 80 being extended to the second succeedingsegment (n 2) and connected through normally closed contacts of aheadway control relay 82B (headway control relays tion of the firstproximity relay 54 because the circuit from the coil 77 of the firstpower control relay 56 to grounded point 58 is interrupted by thecurrently open, third time delay relay 823. A vehicle 11 passing throughthe first segment n then tends to decelerate because of the inherentfrictional drag derived, for example, from its rotating wheels 13, (FIG.1), and thus falls back somewhat from the vehicle preceeding it. Thus,spacing of the vehicles along the guideway 12 is controlled as afunction of the delay times to which the time delay relays are set. Thetime relay relays, associated circuitry, and the power control relays 56thus comprise time responsive switching means operable in response todetection by any respective one of the sensing means of the proximity ofone of the secondary structures, for preventing operation of at leastone primary element 40 spaced at predetermined distance, or multiplie ofcircuit segments, in the second direction along the guideway from therespective sensing means actuated by a vehicle during the preselectedtime period following detection by the respective sensing means of theproximity of a respective secondary structure. Preferably, the timeresponsive switching means prevents operation of a primary element (40),FIG. 5, spaced in the second direction beyond a second primary element(40A) spaced between the respective sensing means (528) and the firstprimary element (40), in order that the first primary element 40 willremain energized until a vehicle 11 powered thereby is completelypassed. The proximity sensors 52 thus actuate the proximity relays 54and the power control relays 56 when the secondary structures 20 of thevehicles enter a zone or region approximately bounded by first andsecond, parallel planes perpendicular to the guideway 12 and extendingthrough the first and second end portions 44, 45 of the respectiveadjacent primary element 40, since several inches of spacing between therespective proximity sensors 52 and the respective, correspondingprimaries 40 is sufficient to permit actuation of the control means,i.e., the respecfive proximity relay 54 and power control relay 56, bythe time the UM secondary reaches the area in approximate verticalalign-ment with the respective LIM primary 40.

This method of time responsive" headway control provides the importantadvantage that the spacing of the vehicles corresponds directly withtheir velocity. that is, it follows that a given delay time provides agreater spacing for vehicles passing at high velocity than for thosetraveling at a low velocity. The efficiency of the system is thusgreater than one dependent upon a predetermined, minimum headwayspacing, in that when the vehicles are traveling at lower velocities atwhich less headway spacing is required, their spacing is automaticallyreduced. Such low speed operation may be required, for example incongested areas, approaches to stations, or the like, and the speed ofthe vehicles is reduced in such areas by the utilization of primaryelements 40 having greater pole pitch, or by reducing the frequency ofthe 3-phase power applied to those primaries. A further advantage of thedisclosed method of headway control is that the vehicles are not sharplydecelerated by the non-energized LIM primaries, as they are upon theapplication of positive braking devices, but are gradually deceleratedat a comfortable rate. Additionally, the spacing of the vehicles may beeasily changed by adjusting the delay period of the time delay relays.

The propulsion system 10 may be modified for adaption to transportationsystems of various types. For example, the control circuits 51 may besimplified by the elimination of the headway control mechanism and thereversing relays in systems or portions of a system wherein only verylow speeds are required. In such a system, the proximity relays 54A arepreferably connected through respective, additional leads (not shown) inparallel with leads 76A, 116A, extended to the respective power controlrelay 56 preceeding the proximity sensor (52A) for simultaneouslyenergizing two LlM primaries, 40, 40A, to ensure that the UM primariesremain on until the vehicle has passed.

Permanent magnets (not shown) are preferably employed in portions of theguideway which are inclined downwardly or in guideway sectionspreceeding station areas, for providing a decelerative force to thevehicles in such sections to maintain proper spacing and to provide afurther safeguard for the system in the event of a power failure. Suchuse of permanent magnets as braking means is generally known in the art.

It should be understood that, in normal operation, control and spacingof the vehicles is accomplished entirely by the action of the time delayrelays, the phase sequence reversing apparatus being employed only incase immediate, sharp braking of the vehicles is required. If suchemergency braking is required, however, as in the case of a vehiclestalled upon the roadway in front of an approaching vehicle, thereversing relay acts to bring the approaching vehicle to a completestop. If for example, a vehicle is stalled in segment (n 2), the thirdproximity sensor 52B will have actuated proximity relay 54B, closingswitch element 62B and permitting positive potential to be con-ductedvia lead back to the coil 106 of the first reversing relay 57. When anapproaching vehicle then enters segment n and actuates the firstproximity sensor 52, the first proximity relay 54 and the first powercontrol relay 56 are actuated to conduct power to LlM primary 40, butthe first reversing relay 57 causes such power to be reversed inpolarity at two of the coils of the primary 40, and to produce amagnetic flux which tends to oppose the forward movement of the vehicleand to strongly decelerate the vehicle, bringing it to a complete stopbefore it collides with the stalled vehicle. The switch element 78 ofthe reversing relay 57 closes the circuit to ground through leads 85,87, and 88, thus conducting current through coil 77 of power controlrelay 56 in spite of the open switch 121B of the third time delay relay828. The reversing means thus comprises a means overriding any operationof the time responsive switching means 828, to prevent operation of therespective primary element 40 to which reversed power is applied. Thereverse thrust thus exerted would tend to drive the vehicle in reverseif it were not then opposed, and such a condition is preferablyprevented by the installation of a ratchet mechanism or the like on oneof the wheels of the vehicles for preventing rearward mvoement of thevehicle, Prefer-ably, a mechanism such as the one-way clutch 124illustrated in FIG. 4 is employed. The clutch is mounted coaxiallywithin a wheel 13 of each vehicle 11, with the vehicle wheel beingaffixed to an outer, circular, rotatable member 125 which is rotatablein the direction indicated by arrow 126 about a fixed, central element127. Rotation 82B, 82, and 82A to be described in more detail below) theclosed circuit continuing through return lead 84 to lead 85 (FIG. 7)through a normally closed, thermal protection switch 86 mounted on thefirst LIM primary 40, and finally returning to grounded point 58 throughsuccessive leads 87 and 88. Current passing through the coil 77 of thefirst power relay 56 is operable to close the switch elements 90 of thepower control relay 56, which is suitably of the type manufactured bythe Square D Company as Class 8536-SDGl. Three switch elements 90 of thepower control relay 56 are connected, through wires 92, 93, and 94, torespective, 3- phase power supply conductors 65A, 65B, and 65C; whenclosed, the switch elements 90 connect wire 92 through wire 103 to oneterminal of the first LIM primary 40. The other wires 93, 94 areconnected to wires 97 and 96, respectively, which are conducted to theother two terminals of the LIM primary 40 through the reversing relay 57and subsequently through wires 104 and 105, respectively. The reversingrelay 57 is, in its illustrated, normal condition, connected to supply3- phase power to the first LIM primary 40 in a sense, i.e., phasesequence, which will cause the primary element to react with an adjacentsecondary structure (FIG. 1) to urge the secondary structure in aforward direction. If reversing relay 57 is actuated, however, thecontacts of the reversing relay 57 are reversed in position, and therelay 57 acts to reverse the polarity of cur rent supplied through leads104 and 105 and to thus cause the primary element 40 to urge an adjacentsecondary structure 20 rearwardly, causing a fairly sharp decelerationof a vehicle 11 associated with the secondary 20.

The reversing relay 57 remains in its normal, nonactivated positionuntil current is conducted through its coil 106, from input lead 107through grounded lead 88. Input lead 107 is connected, through aplurality of rectifying diodes 108, 109 directioned to supply positivepotential only to lead 107, to reverse signal leads 110 and 111 whichextend, respectively, to the proximity relays 54B of successivepreceeding circuit seg ments beginning with segment (n 2) which isspaced, from segment n beyond the next adjacent preceeding segment (n1). Lead 110, for example, extends to proximity relay 54B of segment (n2) and is connected to the output terminal of normally open, switchelement 62B. The other side of switch element 62B receives a positivepotential through lead 1128 connected to the positive supply conductor73. The other reverse signal lead 111 extends to the next preceedingsegment (n 3), not shown in the drawing. The terms preceeding andsucceeding are used in the specification in referring to physicallocation (in front of, to the rear of) rather than to the order in time.

When reversing relay 57 is actuated, its lowermost switch element 78closes and completes a circuit to ground 58 through leads 85, 87, and 88from the coil 77 of power control relay 56.

Referring again to the circuit of segment n and with primary referenceto FIG. 7, a latching circuit 114 is provided connected to the fourth(lowermost) terminal 115 of the first power control relay 56 wherebyonce the relay switches 90 are closed, positive DC current is conductedto the relay coil 77 through leads 116, 117, 75, and 74 from thepositive DC supply conductor 73 independently of the position ofswitches 61, 62 of the proximity relay 54. The purpose of the latchingcircuit 114 is to keep the power relay 56 closed when switch 53 isopened after the vehicle passes the first proximity sensor 52. The firstLIM primary 40 would otherwise be deactivated prematurally, and wouldnot react with an adjacent LIM secondary 20 after the rear end portionof the secondary had passed the first proximity sensor 52.

The latching circuit 114 remains latched until the power control relay56 is deactivated by the action of the headway control relay 82B ofsegment (n 2) when the secondary structure 20 trips the proximity sensor528, which will now be described.

The normally closed, headway control relay 82 is connected with its coilin series between ground and a lead 118 connected to lead 76 and hasleads 119, 120 connected in series with its normally closed switchelement 121 and extending rearwardly to the second preceeding segment(not shown). For the purpose of ex plaining the headway control relay82, reference is made to the corresponding headway control relay 82B ofthe third segment (n 2) which has its coil con nected between lead 768between relays 54B and 56B and ground. As will be seen, the thirdheadway control relay 828 controls the operation of the power controlrelay 56 of the first segment n. The headway control relays 82, 82A, 82Bare of the time delay type operable to open respective, associatedswitch elements 121, 121A, and 121B immediately upon actuation, and toremain open for a predetermined time thereafter. Preferably, the timedelay relays 82, 82A, 82B are of the type wherein the delay period maybe adjusted at will. An example of such a time delay relay is thatmanufactured by the Allen Bradley Company under part number 849A-ZAD 24.

In operation, when a vehicle 11 (FIG. 1) passes over the first proximityrelay 52, the first proximity sensor 54 is actuated, and, as has beenpreviously described, causes the first power control relay 56 to closeits switch elements 90 and conduct 3-phase power to the first LIMprimary 40 in a phase sequence which energizes the LIM primary to urgethe vehicle 11 in a forward direction, assuming the first reversingrelay 57 has not been actuated to reverse the polarity of the suppliedpower. It will be recalled, however, that acutation of the first powercontrol relay 56 depends upon completion of the circuit (describedabove) to grounded point 58 from the coil 77 of power control relay 56.The circuit to ground passes through leads 84 and connected through thenormally closed switch element 1213 of the third time delay relay 82B ofsegment (n 2). The third time delay relay 82B remains in its closedcondition unless it is actuated by a positive potential received throughlead 1228 from lead 768 from the third proximity relay 548. Such apotential exists when the third proximity relay 543 has been actuated bya vehicle passing over the third proximity sensor 52B. Because of itstime delay function, previously described, the third time delay relay82B remains open for a selected interval of several seconds after avehicle has passed segment (n 2). Therefore, if a vehicle passes overthe first proximity sensor 52 while another vehicle is adjacent thethird proximity sensor 528, or if another vehicle has passed the thirdproximity sensor 523 within the delay period during which the third timedelay relay 82B remains open after initial actuation, the forst powercontrol relay 56 is not actuated by actuathereof in the oppositedirection tends to move the bearings 128 into a locked positionindicated at 129 and to prevent further rotation. Inasmuch as the use ofsuch mechanisms is generally known, further description thereof is notconsidered necessary.

The reversing relay 57 of segment n will be actuated by a vehicle insegment (n 2), through lead 110, or by a vehicle in segment (n 3) (notshown) through lead 111. In LIM systems of higher speeds, however, itmay be desirable to provide additional protection by actuating the firstreversing relay 57 if a vehicle is spaced forwardly of segment n by aneven greater distance. This is accomplished, in an alternativeembodiment (not shown), by adding additional leads extending from theproximity relays 54 of those segments (n 3, n 4, etc.) and extending theleads back to the first reversing relay 57 through respective,additional diodes connected in parallel with diodes 108 and 109.Additional redundancy of the time delay portion of the circuit 51 mayalso be provided by connecting the time delay relays 82 to the powercontrol relays of additional segments preceeding the one spaced twosegments behind. Such additional connection is provided, in analternative embodiment, by employing time delay relays 82 havingadditional switch elements, and conducting leads from the additionalswitch elements to the power control relays three or more segmentspreceeding (e.g., from relay 8213 to (n l), (n 2), etc.)

With reference now to FIG. 5, the spacing of the LIM primary elements40, 40A, and 40B of respective, corresponding pairs 49 with theirrespective first end portions 45 spaced equally along the guideway, andthe use of primaries of approximately equal lengths, permits theapplication of an approximately equal, forwardly directioned, magneticdriving force to the secondaries even though successive ones of theprimary elements 40, 40A, and 40B are not positioned end to end alongthe guideway or in close proximity with each other along the guideway,as they have been in some prior systems. Thus, the great expense ofpurchasing and installing LlM primary elements extended substantiallycontinuously along the guideway is avoided. In the preferred embodiment,illustrated in both FIGS. 5 and 6, wherein the respective first endportions of the primary elements of respective corresponding pairs 49,48 are spaced from each other by a distance substantially equal to thelength of the secondary structures 20, the

spaced LIM primaries 40 are positioned to provide a substantiallyconstant propelling force to a respective secondary structure 20 as itmoves along the guideway 12. When a secondary structure 20 is centeredover two primary elements 40A, 40B of a respective pair 49 as shown inFIG. 5, for example, the equivalent of one primary element is reactingwith the secondary, since the forward end of the secondary structure ispositioned over approximately one half of the secondary 40B and over onehalf of the rear secondary 40A. In the embodiment shown in FIG. 6, thesecondary structure 20 is continuously urged forward by the equivalentof one of the shorter primaries 40, 40A and additionally, by theequivalent of one of the longer secondaries 46. The control circuit 51(FIGS. 7-9) operates to energize the successive primaries 40, 46, 40Asequentially, since the respective segments n (n l (n 2) of the controlcircuit 51 are actuated by successive proximity sensors adjacent each ofthe successive LIM primaries 40, 46, 40A.

The combination of the above-described spacing of the primary elementsrelative to the preferred length of the secondary structures and thearticulated framework 25 supporting the LIM secondary elements 21 ineach secondary structure 20 (FIG. 3) provides further economic benefitsin that secondary structures 20 of considerable length may be employedsuccessfully over a less-than-perfectly constructed guideway, thudpermitting the spacing of the LIM primaries 40 to be greater than thatrequired if rigid, single element secondaries are employed. Thus, in theembodiment of FIG. 5, the primaries 40 are extended along only a smallpercentage of the guideway, the length of each secondary structure beinggreater than twice the combined length of the primary elements 40, 40A;40A, 40B of pairs 49 of corresponding primaries.

It can thus be seen that the present system provides the advantagesinherent in the fixed primary, movable secondary, linear inductionpropulsion systems while greatly minimizing many of the economicdisadvantages of such systems.

The primary elements and their associated control circuitry are safelyenclosed beneath the surface of or alongside the guideway, thuspreventing deterioration of the control elements from vibration andweather conditions and minimizing the likelihood of vandalism. Moreover,the requirement for slidable electrical brushes and exposed power railsextended alongside the guideway is completely eliminated, along with theattendent safety and maintenance problems of such power supply systems.Economic advantages are thus derived from the elimination of both theinitial costs of such systems and the avoidance of continuousmaintenance thereof.

Current is conducted to only the LIM primaries adjacent respective onesof the LIM secondaries, and power consumption is therefore minimized.Control of headway and velocity is achieved by control circuitryenclosed safely within or alongisde the guideway, and does not dependupon braking devices or operators aboard the vehicles. Headway can bevaried conveniently by a simple adjustment of the time delay relays, andfinally, the combination of time-dependent headway control means anddistance-related emergency braking means permits close spacing of thevehicles for providing a high rate of passenger flow. This last featureis of great importance in personal rapid transit systems, in that therelatively small vehicles and low speeds of such systems require closespacing of the vehicles if economically practical levels of passengervolume are to be achieved.

While only one embodiment of the invention, to gether with modificationsthereof, has been described in detail herein and shown in theaccompanying drawing, it will be evident that various furthermodifications are possible in the arrangement and construction of itscomponents without departing from the scope of the invention.

What is claimed is:

1. For a transportation system of the type having movable structuresadapted to follow a guideway, a plurality of linear induction primaryelements fixedly mounted in the guideway, mutually spaced along theguideway, and having respective first and second end portionsdirectioned in first and second directions, respectively, along theguideway, and elongated, linear induction secondary structuresconnected, respectively, to each of the movable structures, a controlsystem comprising:

a plurality of sensing means, each corresponding to a respective primaryelement and each comprising means operable for detecting the proximityof one of the secondary structures to the respective primary element;and

control means, operatively associated with the proximity sensing means,for conducting multi-phase electrical power to any of the primaryelements when any portion of one of the secondary structures lies withina region approximately bounded by first and second, parallel planesperpendicular to the guideway and extending through the first and secondend portions, respectively, of a respective primary element, for urgingthe respective secondary structure in the first direction, the controlmeans further including time responsive switching means, operable inresponse to detection by any respective one of the sensing means of theproximity of one of the secondary structures, for preventing operationof at least one primary element spaced a predetermined distance in thesecond direction along the guideway from the respective sensing meansduring a preselected time period following detection by the respectivesensing means of the proximity of a respective secondary structure.

2. The apparatus of claim 1, wherein the time responsive switching meanscomprises means for preventing operation of a first primary elementspaced in the second direction along the guideway from a second primaryelement interposed between the first primary element and the respectivesensing means.

3. The apparatus of claim 1, further comprising reversing means forapplying multi-phase electrical power, in a phase sequence causingmagnetic forces to be produced opposing movement of the secondaries inthe first direction, to a primary element adjacent a respective one ofthe secondary structures when another respective secondary structure isadjacent at least one sensing means spaced, in the first direction, fromthe respective primary element, the reversing means comprising meansoverriding any operation of the time responsive switching means toprevent operation of the respective primary element to which reversedpower is applied.

4. The apparatus of claim 3, wherein the movable structure is providedwith means preventing movement thereof along the guideway in the seconddirection.

1. For a transportation system of the type having movable structuresadapted to follow a guideway, a plurality of linear induction primaryelements fixedly mounted in the guideway, mutually spaced along theguideway, and having respective first and second end portionsdirectioned in first and second directions, respectively, along theguideway, and elongated, linear induction secondary structuresconnected, respectively, to each of the movable structures, a controlsystem comprising: a plurality of sensing means, each corresponding to arespective primary element and each comprising means operable fordetecting the proximity of one of the secondary structures to therespective primary element; and control means, operatively associatedwith the proximity sensing means, for conducting multi-phase electricalpower to any of the primary elements when any portion of one of thesecondary structures lies within a region approximately bounded by firstand second, parallel planes perpendicular to the guideway and extendingthrough the first and second end portions, respectively, of a respectiveprimary element, for urging the respective secondary structure in thefirst direction, the control means further including time responsiveSwitching means, operable in response to detection by any respective oneof the sensing means of the proximity of one of the secondarystructures, for preventing operation of at least one primary elementspaced a predetermined distance in the second direction along theguideway from the respective sensing means during a preselected timeperiod following detection by the respective sensing means of theproximity of a respective secondary structure.
 2. The apparatus of claim1, wherein the time responsive switching means comprises means forpreventing operation of a first primary element spaced in the seconddirection along the guideway from a second primary element interposedbetween the first primary element and the respective sensing means. 3.The apparatus of claim 1, further comprising reversing means forapplying multi-phase electrical power, in a phase sequence causingmagnetic forces to be produced opposing movement of the secondaries inthe first direction, to a primary element adjacent a respective one ofthe secondary structures when another respective secondary structure isadjacent at least one sensing means spaced, in the first direction, fromthe respective primary element, the reversing means comprising meansoverriding any operation of the time responsive switching means toprevent operation of the respective primary element to which reversedpower is applied.
 4. The apparatus of claim 3, wherein the movablestructure is provided with means preventing movement thereof along theguideway in the second direction.